基于微纳光纤与光子晶体慢光波导的低噪声窄线宽光纤激光技术研究

Single longitudinal-mode fiber laser with high-quality (ultra-high stability, low-noise, narrow-linewidth) has significant applications in the fields such as fiber sensing, coherent communications, microwave photonics, LIDAR detecting, etc. By purposely constructing a large variation of dispersion with frequency in an optical medium, slowing down the group velocity of optical pulses (so-called slow light) is realized, which shows great science significance and application value. This project proposes a new method where the micro/nano fiber and W1-type (missing one air-hole line) photonic-crystal waveguide is combined to produce a slow-light waveguide with low-lose, high group-index (ng) and low group-velocity dispersion (GVD). We introduce such a combined slow-light waveguide into the optical resonance cavity to increase the cavity length, the photon lifetime, the Q factor and decrease the Free Spectral Range (FSR). The motivation of this is to obtain a novel fiber laser with high-quality laser output. This research includes: 1) designing and fabricating the combined waveguide with high group-index, low GVD and low insertion loss, as well as studying its slow-light characteristics; 2) analysis of cavity modes and lasing characteristics of the Er/Yb co-doped fiber laser where the slow-light waveguide is embedded in the ring traveling-wave oscillator; 3) laser's system construction, output characteristic measurement, and parameter optimization. With the combination of the micro/nano fiber, photonic crystal waveguide, slow-light and fiber laser technologies, this project will inevitably provide creative ideas and technologies for high-quality and novel fiber laser.

高性能(超高稳定、低噪声、窄线宽)单纵模光纤激光器在相干光通信、微波光子技术和相干雷达探测等领域具有重要应用价值。在光学介质中人为地产生色散随频率的急剧变化，从而获得群速度减慢的慢光效应和技术具有重要的科学意义和应用价值。本申请提出了将微纳光纤与W1型(缺失一行空气孔)硅基光子晶体波导结合产生低损耗、高群折射率ng、低群速度色散GVD的复合型慢光波导的新方法，并将该慢光波导植入光学谐振腔中(从而增大谐振腔的腔长、光子寿命和品质因数Q，减小自由光谱范围)，旨在获得高性能单纵模光纤激光输出。研究内容包括：1)高ng、低GVD、低插入损耗复合型波导的研制及其慢光特性研究；2)慢光波导植入环行行波振荡腔的铒镱共掺光纤激光器的腔模和激射特性研究；3)光纤激光器系统的建立、输出性能测试和参数优化。本项目将微纳光纤、光子晶体波导、慢光和光纤激光技术结合，必将为新型高性能光纤激光器的研制提供创思想和技术。

微纳光纤谐振器以其强倏逝场耦合、高Q因子、强波谱选择特性，在慢光、光信号处理、光通信和激光技术领域具有重要的科学研究意义和应用价值。本项目分别采用微加热器和CO2激光建立了光纤拉锥及其性能实时监测系统，采用单模光纤拉锥制作出了损耗小于0.05 dB，直径在1 μm左右，腰区长度大于20 mm的低损耗微纳光纤；制作出了直径小于1 mm的单环、双环并联、双环串联的微纳光纤谐振器，Q因子大于104,自由光谱范围为0.22 nm；理论上基于FD-BPM方法建立了光纤绝热拉锥理论，模拟分析了微纳光纤外形轮廓对其光传输损耗影响的，获得了低损耗微纳光纤的最佳外形轮廓参数；建立了微光纤谐振器倏逝波耦合的数学物理模型，分析了微光纤直径、微光纤环直径、微光纤环数、微光纤环耦合系数、损耗等相关参数对微光纤谐振器慢光效应的影响。建立了微光纤环谐振器慢光测试系统，最大相对慢光延时可达30 ps。将所制作的微纳光纤慢光微环谐振器置于光纤环形谐振腔中(从而增大谐振腔的腔长、光子寿命和品质因数Q，减小自由光谱范围)，实验上获得了C波段高稳定的单波长的掺铒光纤激光输出，中心波长1558.818 nm，3dB线宽0.0149 nm，边模抑制比大于30 dB，输出激光功率最大起伏小于0.85 dB。提出了在光纤激光器系统中加入微小空气腔，通过加强菲涅尔反射效应增强光纤中的四波混频，降低布里渊斯托克斯光的阈值，实现了C波段稳定的多波长光纤激光输出，波长数达41条，激光功率达-19 dBm。本项目有机结合了微纳光纤谐振器、慢光和光纤激光技术，必将为新型的高性能光纤激光器的研制提供创思想和技术基础。